Signaling system



R. s. OHL 1,753,443

SIGNALING SYSTEM Filed Oct. 8, 192e L; EPE L2 IN V EN TOR.

A TTORNEYS.

Patented Apr. 8, 1930 vUNITE- STATES RUSSELL S. OEL, OF NEW YORK, N. Y., ASSIGNOR T AMERICAN TELEPHONE AND GRAPH COMPANY, A CORPORATION OF'NEW YORK I TELE- SIGNALING SYSTEM Application filed October 8, 1926. Serial N o. 140,389.

of signals of high frequency.

'It is well known that in order to attain good voice quality in voice frequency signaling systems whentransmittting voice fre` quency signals in the form of high frequencyl energy over a considerable distance, it is necessary to maintain they high frequency or carrier wave very constant in frequency. In

' order to receive and detect the energy present in, for example, a single side bandof such high frequency energy,- lit'is necessary to introduce some local frequency which may be employedto beat with'the side band in order that the low or voice frequency signals maybe faithfully reproduced.

A common `practice for receiving, a high frequency modulated signal is firstto change the frequency of thefsignal to another frequency 'lowered in the frequency spectrum, which may be amplified more easily than the isrt high frequency originally received, and second, to detect the signal from the intermediate frequency. This is done bythe wellknown means of beating the received high fre.

quency signal with the unmodulated, sinus- *30 oidal frequency of a local oscillator to produce an intermediate frequency which can then easily be amplified. One can readily see that'the intermediate frequency should vary no more than the higher frequency originally l received, if it is essential to maintain high qualitystandards throughout the system.

`In this invention there will be shown, merely for lthe sake of illustration, an oscillatordetector arrangement which will be connected to an antenna system timed to receive a side band of=high frequency signals in order kto change the received band ofv signals into another and'similar' band of signals changed in the frequency spectrum. Another oscillator will supply the frequency to beat with the latter band lof signals in order to derive the original or low voice frequency signals therefrom. The latter oscillator will have a piezoelectric device connected thereto to carefully adj ust the frequency Yof lthe oscillations sustained thereby and, besides, to control these oscillations at the particular frequency desired. By beating the band of signals which is changed in the frequencyv spectrum,with the oscillations sustained by the oscillator wliichare 'controlled and varied bymeans of 'the piezo-electric device, the low frequency v signals originally present in the form of high frequency energy are faithfully detected and reproduced.`

Accordingly it is an object of this invention to associate the outputvofan oscillator with'aband of' high frequency energy, so thatA by controlling and varying the frequency of the 'oscillator as conditions necessitate, the original band of signals will be faithfully reproduced with considerably greater accuracy than has heretofore been possible.

Another of the objects of this invention is to reform a side `band of high frequency energy intoa-corresponding band of signals-in a different'position in the frequency spectrum and .tov beat the latter band of signals with the oscillations'sustainedby an oscillator/having a piezo-electric device associated therewith vfor controlling and varying the frequency thereof in order to reproduce the signals orig-l` inally present inthe side rband of high frequency p energy, all of which yis accomplished with considerably greater accuracy than'has heretofore been possible. l

, while the invention will beV pointed out with particularity inthe appended claims,

the invention itself, both as to its further ob- ]ectsand features, will .be better understood from the detailed description hereinafter, following when read in connectionwith the accompanying drawing showinggone embodi-A ment of the invention, merely for the purpose of illustration. i.

Referring tothe drawing, an antenna sys-y tem is shown comprising anantennaNand ground, whichantenna system 'isi-employed to receive a sideband of very high vfrequency energy. rlhis side band of high frequency energy is impressed upon fan oscillator-detectorV CD1. This oscillator-detector OD1 generates a high frequency wave which is used to beatvwith the side band of high ,frequency signals received-bythe antenna syssov teni. Accordingly there will appear in the output of the oscillator-detector' CD1 another band of signals corresponding to the band of signals received by the antenna system but which is changed in the frequency spectrum. It will be understood that this oscillator-detector OD1 may be of any well-known type, but that it is preferably of the vacuum tube type. The oscillator-detector CD1 is connected to an intermediate frequency ainplifier A which amplifies the band of` signals transmitted by the oscillator-detector CD1, which, of course, corresponds to the side band of high frequency signals received by the antenna system. After amplification bythe intermediate frequency amplifier A, the band of signals transmitted thereby is impressed upon another' detector D2.

The reference character C designates an oscillator which sustains oscillations of a high frequency. This oscillator may be of any well-known type but it is preferably of a vacuum tube type. This oscillator may also be of the untuned type and may, of itself, vary in frequency considerably from its characteristic frequency. In order to maintain the frequency of the oscillator O constant in frequency within very narrow limits and in order to render the frequency characteristic of the oscillator O adjustable as may be found desirable, a piezo-electric device is associated therewith which device comprises a piezo-electric crystal PE which -is placed between two conductive electrodes L1 and L2. The conductive electrode L1 is preferably rigidly fixed to an adjustable thumb screw T so that as the thumb screw is moved inwardly or outwardly, a correspondingchange will take place in the distance between the piezoelectriccrystal PE and the conductive electrode L1. Obviously, the width of the dielectric, such, for example, as air, between the conductive electrode L1 and the piezo-electric crystal PE, may be changed by manipulation of the thumb screw T. The piezo-electric device, of course, may be located in a boX or other container which may be made of bakelite,hard rubber or other insulating material. Means may also be provided for accurately determining the displacement of the thumb screw T. It is to be understood that it is within the scope of this invention to provide any means whatsoever for rendering a fine adjustment of the space between the piezoelectric crystal PE and one or both of its conductive electrodes so that in effect the frequency characteristic of the piezo-electric crystal may be carefully adjusted and varied with considerable precision.

In an oscillator with which a piezo-electric device is associated, which comprises a piezoelectric crystal vibrating between conductive electrodes, it has been found that the oscillator may be controlled and varied as to frequency by adjusting the size of the gap existing between the piezo-electric crystal and its conductive electrodes. Generally, as the space between the crystal and its conductive electrodes changes, a corresponding change is produced in the frequency of the oscillations sustained by the oscillator. More particularly, as the distance between the piezo-electric crystal and its conductive electrodes is increased, the frequency of the oscillations sustained by the oscillator will,

under normal conditions, also be increased, and vice versa. This is exactly what takes place when the piezo-electric device, comprising the piezo-electric crystal and the conductive electrodes L1 and L2, is associated with the oscillator O. Briefly, the frequency of the oscillations sustained by the oscillator O may be controlled and varied by the piezoelectric device with precision.

Oscillations sustained by the oscillator O, which are controlled and varied by the piezoelectric device, are also transmitted tothe detector D2. This detector may be of any well-known type but it is preferably of the vacuum tube type. The frequency of the oscillator, thus controlled and varied, beats with the band of signals amplified and transmitted by the intermediate frequency amplifier A, so that the original signals which were present in the side band of high frequency energy received by the antenna system are accurately detected by the head set R, It will be fairly obvious that if the oscillator O were not controllable and variable as to frequency by a device such as is shown here, i. e., a piezo-electric device, the original signals would not be faithfully reproduced. By associating the piezo-electric device with the oscillator O, it is possible to maintain such a high quality in transmission as has heretofore not been possible. j

lt will be understood that while this inven- -tion has been shown herein for the purpose of illustration as a double detection system, the principles of this invention may be applied to numerous other systems and to various embodiments of such systems without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a signaling system, the combination of means for receiving a side band of high frequency energy characteristic of speech signals, means for producing another band of signals corresponding to the received side band but changed in the frequency spectrum, an oscillator generating a wave to be beaten witn the band of signals changed in the frequency spectrum, a piezo-electric structure connected to the oscillator for controlling the frequency of the generated wave, means for varying the vibratory period of the piezoelectric structure so as to correspondingly vary the frequency of the wave generated by the oscillator, and means for beating the piezo-electrically controlled and varied frequency of the oscillator with the bandof signals changed in the frequency spectrum in i order to accurately reproduce the speech signa s.

A2. In a signaling system, the combination of means for receiving a band of signals of high frequency representing voice frequency signals, an oscillator-detector to produce from said band of signals another and similar band of signals changed in the frequency spectrum, an oscillator, a piezo-electric structure includlng a piezo-electric crystal and two spaced electrodes, said piezo-electric structure being coupled to said oscillator, means including a screwethreaded member forvarying the spacing of the electrodes of the piezo-electric structure in order to change the frequency of m the current produced by the oscillator coupled thereto, and means for beating thepiezoelectrically controlled and varied frequency of the oscillator with the band ofv signals changed in the frequency spectrum to accurately derive the original Voice frequency signals.

In testimony whereof, I have signed my name to this specification this 6th day of October, 1926. f

RUSSELL S. OHL. 

